The invention relates to an optical scanner, more particularly an optical scanner suitable for scanning bar codes, comprising a laser source for generating a laser beam, a first deflector for deflecting the laser beam towards an array of reflectors, the first deflector and the array of reflectors being rotatable relative to each other about a first axis, drive means for providing a rotation, and at least one detector for detecting backscattered light. Such an optical scanner is known from U.S. Pat. No. 4,699,447.
In the known optical scanner the array of reflectors is constituted by a basket-shaped array of mirrors. A centrally positioned rotatable mirror deflects the beam generated by a laser source towards the mirrors of the basket-shaped array, the laser beam sweeping across the mirrors so as to generate scanning lines. From each mirror of the array the laser beam is subsequently directed towards the bar code to be scanned. As the scanner during operation is usually pointing at the bar code to be scanned, this bar code will be located on or near the axis of the scanner, this axis in the known scanner being the rotational axis of the centrally positioned rotatable mirror. Since the mirrors of the array are necessarily located off-axis, the laser beam reflected by the mirrors of the array will be slanted relative to the axis of the scanner so as to be directed towards the axis and thus towards the bar code located on this axis. Due to this slant of the reflected beam, however, there will be only a limited region in which the reflected beam is located near the axis and thus on the bar code. This region, which constitutes the effective scanning region, will be located at the intersection of the reflected beam and the axis. At a point nearer to or further away from the scanner and thus removed from this intersection, the reflected beam will not be able to scan the bar code since it will not cross all the bars of the code. The effective scanning range of this known scanner is therefore limited to the region where the reflected laser beam intersects the axis, since the laser beam will not be able to (completely) scan a bar code outside this region. Placing the bar code off-axis is not a solution, since in that case the light reflected by one or two mirrors may impinge upon the code, but the light reflected by the mirrors opposite those one or two mirrors will miss the bar code altogether, resulting in an incomplete scanning pattern and a decreased chance of reading the code correctly. This problem is aggravated by the fact that in the typical scanning pattern the most effective region for reading a bar code is around the centre of the pattern. Preferably, the scanner should be able to provide a scanning pattern of which at least the central region is independent or virtually independent of the scanning distance, i.e. independent of the distance of the bar code from the scanner.
In U.S. Pat. No. 5,177,347 a bar code reading apparatus is described in which, a laser beam generated by a laser source is directed to a first mirror through a hollow shaft of a motor The first mirror directs the laser beam to a mirror array. The mirror array reflects the laser beam to a second rotation mirror which directs the laser beam in a direction substantially along the path of propagation of the laser beam when impinging upon the first mirror. By this known arrangement the problems mentioned above are largely overcome. However, the use of a motor having a hollow drive shaft is rather expensive.